The present invention relates to a process unit constituting a detachable part of an image forming means of an image forming apparatus such as a copying machine and the like, particularly to a device for detecting life of the process unit, and to a device for detecting opening of a seal of the process unit in which developer is contained in a storage section defined by a seal member prior to use and the seal member is opened for use, and further to a device for detecting attachment of the unit to the image forming apparatus.
It is conventionally known that for the purpose of facilitating maintenance and exchange of expendable parts and the like of an image forming apparatus using an electrographic system etc., a part or the whole of the image forming apparatus comprising a photosensitive drum, a developing device, a cleaning device and the like are integrated to form a process unit which is detachably attached to the image forming apparatus (see, for example, Unexamined Japanese patent publication No. 56-128958).
Such a process unit is, as an expendable, replaced by a new one for ensuring the quality of a copy image when the process unit is used up to lose its life. Then, a means for detecting the life of the process unit and informing users of the same is known which is adapted to measure the amount of used transfer paper passing through the process unit or count the number of rotations of a photosensitive drum, and give a visible indication when the obtained value reaches a predetermined value which means a predetermined life level of the process unit (see, for example, Unexamine Japanese patent publication No. 58-152263).
According to the abovementioned life detecting system, however, for example by making a large amount of copies of an original having a high density, toner is consumed before visible indication of the life of the process unit is made on the basis of the counted rotation number of the drum, which makes it difficult to detect the life of the process unit. Besides, poor copied images are produced, and so-called carrier attraction occurs; that is a carrier is attracted to a latent image on the photosensitive surface, transferred onto a transfer paper, and further slipped in a fixing device, thereby resulting in damage to a heat roller thereof, and causing troubles in temperature control by means of a thermister.
Further, in a copying machine etc. in which the density of the toner contained in a developing device is detected and the amount of toner supply is controlled to obtain a given toner density, if the toner density is below a given value, a process unit may be judged to lose its life due to toner consumption. In this case, however, without choosing the best timing for the judgement, the toner density cannot be accurately detected by means of a sensor, and sometimes it becomes difficult to accurately detect the life and the detection takes too much time, thereby lowering the efficiency.
Furthermore, in a conventional process unit in which at least a developing device is included in a casing, for the purpose of preventing the dispersion of developer held in the developing device as well as preventing the photosensitive surface from being roughed by the dispersed developer, the developer is contained in a space of the developing device defined by a seal member when the process unit is in a packaged state prior to use, and by opening or peeling off the seal member for use i.e., at the time of setting the process unit, the developer is supplied into a developer chamber where a developing roller of the developing device is located so that images can be formed (see, for example, Unexamined Japanese patent publication No. 59-61861).
In conventional arts, however, since no means is provided for detecting opening of the seal member, a user sometimes forgets to peel off the seal member and the image forming operation is carried out with the seal member being still unopened. In such a case, naturally no image is formed and the transfer paper is wasted as a miscopy or blank copy.
Further, since a conventional image forming apparatus is not provided with any means for detecting attachment of the process unit to the apparatus as well as detecting connection of a predetermined control system, the apparatus with the process unit being unattached still appears to be in an image forming or copying state.
Therefore, if the copying operation is carried out with a process unit being unattached, a jam of paper often occurs, and even if the paper can be passed through, naturally no image is formed, so that transfer paper is wasted as a miscopy or blank copy. For eliminating such problems, a switch may be provided for detecting attachment of the process unit, which makes, however, the apparatus expensive.